A four-year project by nearly 400 ecologists has produced a reanalysis of global biodiversity that reveals which regions are the most important, and the most threatened.

The effort, coordinated by the non-profit organization Conservation International, adds 9 biodiversity hotspots to the 25 originally recognized in 20001. A hotspot is a region with 1,500 unique, or endemic, plant species (equivalent to 0.5% of the global total) that has lost at least 70% of its original habitat owing to, for example, deforestation or invasive species.

The 34 hotspots house three-quarters of the world's most threatened mammals, birds, and amphibians. About half of all plants and 42% of land vertebrates are found only in these regions. The combined area of the hotspots was once equivalent to Russia plus Australia; now it is slightly larger than India.

“There has to be some global response to conserving biodiversity.”

Thomas Brooks Conservation International

The book presenting the work, Hotspots Revisited, is aimed at key decision-makers, says Thomas Brooks, senior director of the department of conservation synthesis at the Washington-based Conservation International.

"The greatest concentration of biodiversity occurs in those countries that can least afford to pay for its conservation," says Brooks. "It is clear that there has to be some global response to conserving biodiversity worldwide."

Tool for all

As well as a tool for policy-makers, Brooks hopes that the book will improve communication between agencies. The revised hotspot boundaries now match those of the 825 ecoregions defined by the WWF, the global conservation organization. These ecoregions divide the world's land into areas containing distinct sets of species. The unified approach will help conservation groups prioritize their efforts.

The raw data compiled by the researchers, showing each region's biodiversity and the threats that face it, will be available to the public, via an online database listing the species indigenous to each hotspot.

The nine new hotspots include the mountains of central Asia and the east Melanesian islands. Some, such as the Himalaya region, were previously subdivisions of identified hotspots. Another addition was the deserts of the Horn of Africa. "This was the most surprising of them," says Brooks. The region hosts more endemic plant species than researchers had suspected.

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This hotspot is centered to the east of the Ethiopian Highlands and is one of only two spots that are entirely arid. The region covers 579,000 square miles, and contains 2,500 endemic plants. The region is known for its trees, which provide some of the Horn of Africa's most famous commodities, including frankincense, myrrh and cinnabar.

Overgrazing, uncontrolled hunting and other human activities threaten the rich plant, reptile, and bird diversity of this area. Only 5% of the Horn's original habitat is in pristine condition.